1. Field of the Invention
The present invention relates to a method of and an apparatus for assembling mechanical units having a body with a plunger-like rod. More particularly, this invention concerns both a mechanical unit assembling method for assembling a plunger-like rod and a body in which the plunger-like rod slides so as to provide a mechanical unit. This invention also concerns an apparatus for assembling the mechanical unit.
2. Description of Related Art
A mechanical unit having a body and a reciprocal plunger-like rod installed for sliding movement in the body conventionally includes hydraulic control valve units. Each of the control valve units includes a valve body and a spool as a reciprocal plunger-like rod and typically forms an important element of a hydraulic control circuit of an automatic transmission for automotive vehicles. The valve body is typically formed with an axial valve bore including a plurality of coaxial cylindrical bore sections having different inner diameters and coaxially arranged continuously along the axial length of the valve bore. The valve spool is correspondingly configured from a plurality of coaxial cylindrical spool sections having different outer diameters and coaxially arranged continuously along the axial length.
Because of the different diameters of the coaxial cylindrical bore and spool sections and because the accuracy with which the valve spool is fitted into the valve body needs to be sufficient to provide an oil-tight fit between the valve spool and the valve body, it is typical to assemble the hydraulic control valve unit manually. This is because it is quite hard to automate the assembly of the control valve unit. As an easy way to insert the valve spool into the valve body, the valve spool is forced into the valve body after having chamfered the leading edge of the spool so that it is in accord with the valve bore section. Further, if a strong thrust force is applied to the valved spool, it causes wall surfaces of both the valve spool and valve bore and, therefore, the valve body to be vibrated vertically during insertion of the valve spool.
For the purpose of providing a brief description of a conventional automatic valve unit assembling apparatus that will enhance an understanding of the method of and apparatus for automatically assembling hydraulic control valve units of the present invention, reference is made to FIGS. 9 to 11.
In FIGS. 9 to 11, a known automatic valve unit assembling apparatus, as described in Japanese Unexamined Patent Publication No. 3-26432, is schematically illustrated. The apparatus is used to assemble a valve unit 100. This valve unit 100 consists of a valve body 101, a valve spool 47, a coil spring 48 and a plug 49. Specifically, the valve spool 47 and coil spring 48 are inserted into a valve bore 102 of the valve body 101, in order, and then, the open end of the valve body 101 is stopped up by the plug 49. In order to retain the plug 45 in position, a retainer pin 41 is fitted into a retainer bore 103 so that it radially extends in the wall of the valve body 101 and a retainer groove 50 formed in the plug 49. An automatic valve unit assembling apparatus 200 includes a pallet 201 which supports the valve body 101 and moves and positions it at a predetermined assembling station. At the assembling station, after having introduced the spool 47, coil spring 48 and plug 49 into a guide tube 202 by a part feeding and handling device, a shoving device 203, including a floating weight head 204 connected to a cylinder 205, is activated to shove the plug 49 against the coil spring 48 downward until the retainer bore 40 and retainer groove 34 are aligned with each other. While the floating weight head 204 presses the plug 49 down, a retainer insertion device 206, including a cylinder 207, is moved in close proximity to the valve body 101 and inserts a retainer pin 41 into the retainer bore 103 and retainer groove 50 by means of a retainer push rod 207. In order to detect proper insertion of the spool 47, coil spring 48 and spring 49 into the valve body 101 through the guide tube 202, a sensor 61 is provided in connection with the guide tube 202. In addition, a pair of sensors 62 and 63 are provided in connection with the retainer feeder device 206 in order to detect that the retainer pin 41 is in position before and after inserting the retainer pin 41 for detecting proper insertion of the retainer pin 41.
This automatic valve unit assembling apparatus 200 is not readily available for use in connection with valve units in which valve bodies have valve bores comprised of pluralities of different diameters of bore sections and valve spools comprised of pluralities of different diameters of bore sections. Such a valve unit is typically assembled in such a way as to initiate the insertion of a spool into a valve body while bringing the spool into coaxial alignment with the valve bore and then manually inserting the spool while manually keeping coaxial alignment between the spool and valve bore. Accordingly, an important improvement in the valve industry would be in automation so as to provide automatic assembling of valve units with less man power required to perform the necessary work.